The naturally oscillating flow emerging from a fluidic precessing jet nozzle

Abstract

Phase-averaged and directionally triggered digital particle image velocimetry measurements were taken in longitudinal and transverse planes in the near field of the flow emerging from a fluidic precessing jet nozzle. Measurements were performed at nozzle inlet Reynolds and Strouhal numbers of 59 000 and 0.0017, respectively. Results indicate that the jet emerging from the nozzle departs with an azimuthal component in a direction opposite to that of the jet precession. In addition, the structure of the 'flow convergence' region, reported in an earlier study, is better resolved here. At least three unique vortex-pair regions containing smaller vortical 'blobs' are identified for the first time. These include a vortex-pair region originating from the foci on the downstream face of the nozzle centrebody, a vortex-pair region shed from the edge of the centrebody and a vortex-pair region originating from the downstream surface of the nozzle exit lip.

PIV as a Complement to LDA in the Study of an Unsteady Oscillating Turbulent Flow

“…Based on the 0.5(u 2 +v 2 ) 1/2 max contours, the range of emergence angles was estimated to be approximately ±15 about the local jet centreline. This range of angles is two times the value of the minimum phase resolution (±30) in the azimuthal direction (y-z plane) (Wong, Nathan & Kelso, 2008).…”

“…This location, which is also approximately 130 to 150 from the peak in-plane velocity magnitude, resulted in the least influence of the probe and probe holder on the overall flow and was not in the plane of the light-sheet. Experiments conducted in the x'-r plane of the local jet centreline show that the instantaneous jet emergence angle (=53) is relatively constant within x'=40mm (or x'/D 2 =0.625) (Wong, Nathan & Kelso, 2008). Based on the 0.5(u 2 +v 2 ) 1/2 max contours, the range of emergence angles was estimated to be approximately ±15 about the local jet centreline.…”

“…The axial vorticity fields obtained using the phase-precession-direction resolved PIV www.intechopen.com revealed the presence of a number of vortical features near to the FPJ exit plane at x'/D 2 =0.11. (Wong, Nathan & Kelso, 2008). The presence of these structures was further studied by conducting time-averaged surface flow visualisation on the downstream surface of the centrebody using an alcohol-powder mixture.…”

“…The approximate trajectory of the jet centreline in the transverse cross-section initially deflects to the left of the advancing side of the jet, but this deflection is most noticeable after the convergence location at approximately x'/D 2 = 0.58. Wong, Nathan and Kelso (2008) summarised the important features identified in the phaseaveraged longitudinal (x'-r plane) PIV results. These were, a saddle above a reversed flow region near to the exit plane in the central region of the nozzle, a region of separation on the surface of the exit lip whereby the head of the focus points inwards, the mean extent of the flow convergence region, a region of separation on the surface of the exit lip where the head of the focus points outwards, and a conjectured streamline pattern describing the structure of an Edge 2 and an Edge 3 vortices.…”

“…Nevertheless, many details of the flow structure eluded researchers for some two decades and it is only recently that its phase-averaged flow structure has been revealed through the use of laser diagnostic techniques such as phaseaveraged PIV and LDA, complemented by a classical surface flow visualisation technique (Wong, Nathan & Kelso, 2008).…”